I don't know alot about these as I don't use pedals very often. I have installed a passive effects loop in all 3 of my amps to use with a delay pedal. It sounds fantastic in two of them and mediocre in the 3rd one for some reason?? I installed mine between the master volume and phase invertor. Example of a passive effects loop here:http://www.el34world.com/Forum/index.php?topic=597.0
Reading other people's comments on different forums about effects loops, there seems to be some consensus that they work pretty well for delays, reverb, chorus, flanger, etc.... but not so great for distortion or overdrive pedals?
I have not tried these active effects pedals and am not sure where they came from originally???
The ones I looked at tended to have similarities in the layout/topology but differing values in the circuits. I presume there will work, but if someone tries them, perhaps a review can be offered of their effectiveness and tone?
As always, look for errors. You also should try the SEARCH feature to look up posts on the effects loops since it is a frequent topic. Hoffman has a layout/schematic on his Plexi 50w that shows using a passive effects loop between the treble pot and master volume. http://www.el34world.com/Hoffman/images/H50pre.gif